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So I'm using Auto Rig Pro to rig a character, but the knees always bend the wrong way. I've tried moving the bones and the pivot point but it never changes.

enter image description here

I provide the blend file here:

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Make sure the protrusion is facing the direction you want. The protrusion direction will be judged as pole

Right way '<' Wrong way '>'

I used to try align the bones into straight line like | (instead the < > in the pictures), then the generate algorithm would return Error due it doesn't know the protrusion direction.

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The pole target bones must be in front of the knees. It's the red and blue spheres. Your rig has them at the back of the knees. In consequence, the knees bend backward.

I don't know Auto Rig Pro and if it's like Rigify that works with a meta-rig. If it has something like a meta-rig, I recommend fixing the pole's position there. If not, you can edit the current rig and fix it.

You just need to mirror the poles and fix the bone rolls of the knee bones.

Step 1 - fixing the pole position

  • move the 3D Cursor to World Origin (Shift+S)
  • set the Transformation Pivot Point to the 3D Cursor (dropdown menu)
  • select the rig, switch to Edit mode, select the pole bone (c_leg_pole.l) and mirror it along the global Y-axis, which is a scale by -1 (SY-1).

The other pole bones will be moved because X mirroring is enabled. The poles should be now in front of the knees:

pole position

Step 2 - fix the bone rolls. This is necessary so that the mesh is properly deformed and the shin is in front and the calf is on the back and not twisted by 180°.

  • make the last bone layer visible to see the deformation bones
  • select the lower thigh bone (thigh_stretch.l) and change its roll value from -90.478d to 90.478d
  • do the same for the upper shinbone (leg_stretch.l) and remove the -

bone rolls

That's it. Switch to Pose mode, select Individual Origins as Transformation Pivot Point, select bone layer 1 to see the control bones, and give it a try. The knees should be correctly bent.

pose test

Looks like the hair curves are not yet bound to the armature. In Pose mode, they can be made a child of the head bone (head.x) with Ctrl+P Parent To > Bone and they will move with it.

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